1. Field of Endeavor
The invention relates to a method for self-guiding an instrument carrier during in-situ operation in a generator, as well as to an instrument carrier designed for guidance according to this method.
2. Brief Description of the Related Art
Electrical machines transform mechanical energy into electrical energy (generator) and vice versa (motor). Electrical machines usually include a rotor and a stator. The rotor rotates within a bore that is provided in the stator.
The accessibility to stator and rotor is very limited and only possible through a narrow gap between rotor and stator while the rotor is in place. Removal of the rotor of a large electrical machine is costly and time consuming. Especially the outage time of a power plant, which is needed for the removal of a generator rotor, is very expensive and should be minimized to assure high availability of the plant. However, access to the rotor and stator is required for maintenance and inspection of the generator.
To avoid opening of the generator for inspection and maintenance, different devices designed to inspect the generator through the annular gap between stator and rotor, which is also commonly called an air gap, have been proposed. In the WO94/18574 a device that has a complicated sensing and control system to guide the device through the gap is proposed. The main goal of its electrical sensors is to detect the difference in electrical conductivity between generator wedges and iron and to use these as input for the control system. In U.S. Pat. No. 6,100,711, a miniature air gap inspection device is proposed, which has a complex drive and control system and which is remotely operated with the use of a high-resolution camera. Electronic systems that steer a device through the annular gap are cumbersome and a potential source of failure.